Added a default refractive index for air in Material
Fixed a small bug in Sphere's intersect() method that would return false if a ray started inside the Sphere
Removed a normal orientation change in Triangle, the original orientation needed to be preserved to allow for testing of entering/exiting materials
Added Beer's Law calculations to DielectricMaterial, and cleaned up some of the mess.  Still doesn't look right.
Added a default refractive index for air in Material.
Changed some test parameters.
Added a class for axis aligned bounding box hierarchies: AABVHSurface